Symposium CH03—Advances in In Situ and Operando TEM Methods for the Study of Dynamic Processes in Materials III

Judy Cha, Yale University

In Situ TEM Studies of Microstructure Control During Nanoscale Phase Transformation

Written by Henry Quansah Afful

Phase transformation in nanoscale materials often differ from what’s observed in their bulk counterparts owing to differing kinetics and thermodynamics of the transition at these scales. In situ transmission electron microscopy (TEM) techniques make it possible to track the nucleation and growth kinetics in these materials. A knowledge of the kinetics helps to control the phase transformation and resultant microstructure. TEM studies revealed that the crystallization temperature of <50 nm diameter wires of metallic glasses is much higher than in the bulk and attributed this to the absence of pre-existing nuclei. Judy Cha showed that the critical cooling and heating rates for transformation in these materials overlap at these small scales compared to being distinguishable in the bulk. Cha also demonstrated, using TEM, that the growth is 20 times slower when cooling from 900^oC to 420^oC than when heating from 20^oC to 420^oC. In situ TEM can also be used to study the nanoscale nucleation and growth pathways in condensed matter systems. Understanding and controlling the nucleation density opens up several applications for these materials.